摘要:
通过野外露头和岩心观察、薄片鉴定分析,结合测井和录井资料,对柴达木盆地北缘古近系-新近系的沉积相及其特征进行了深入研究。研究表明,该区主要发育冲积扇-辫状河-辫状河三角洲-滨浅湖沉积体系,建立了相应的辫状河相沉积序列及沉积模式、间歇性湖泊沉积相模式。研究区辫状河相发育两套不同地层,中下部广泛发育粒度粗的河床亚相沉积,河漫滩亚相发育不多;而中上部河床亚相沉积较少发育,粒度细的河漫滩亚相沉积则急剧增加。这是由于降水量及气候变化造成冲积扇及河流水动力变化形成的。这种变化还造成沉积物供应速率的变化以及湖平面升降的变化,导致湖盆湖岸线的迁移与河流及三角洲沉积范围的变迁,这种变迁最终造成了沉积序列上粒度粗细的频繁变化及有利储集岩和区域盖层的发育。
Abstract:
Sedimentary facies and models for the Palaeogene-Neogene deposits on the northern margin of the Qaidam Basin, Qinghai are explored on the basis of field outcrops and core observation, thin section examination and well logs. These Palaeogene-Neogene deposits are grouped into the alluvial fan, braided stream, braided delta and littoral-shallow lake depositional systems, and associated sedimentary models for the braided stream and intermittent lake deposits are constructed. In the braided stream deposits, there developed two successions of strata:the coarse-grained river bed subfacies deposits in the middle-lower parts, and the fine-grained overbank subfacies deposits in the middle-upper parts, which are attributed to the hydrodynamic variations on the alluvial fans and in the rivers due to the variations in precipitations and palaeoclimates. These variations also resulted in the changes in sediment supply rates and lake-level fluctuations, lake strandline migration and delta depositional areas, and finally in the frequent alternations in grain sizes of the depositional sequences and facilitate the development of favourable reservoir rocks and cap rocks in the study area.
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